1. Technical Field
The present invention relates to a single port handheld Vector Network Analyzer (VNA) with circuitry capable of providing operation over a very wide bandwidth.
2. Related Art
Handheld VNAs have been available for a number of years, in particular handheld VNAs available include the Site Master™ series manufactured by Anritsu Company of Morgan Hill Calif. Different models of the Site Master™ provide for different frequency operation ranges. For example, the Site Master™ model S331 operates from 25 MHz to 4 GHz, while the model S820 operates from 3.3 GHz to 20 GHz. Both the model S331 and S820 Site Master™ are one port reflectometers used in the evaluation of an antenna and the feed line connecting the antenna to a radio. Unfortunately, a user is forced to purchase two separate units if test frequencies overlap these two models. Inherent fundamental differences exist between the two models disallowing either to cover the frequency band of the other.
The Site Master™ model S331 has a lower frequency operation range and includes components that are similar to those disclosed in U.S. Pat. No. 5,642,039 entitled “Handheld Vector Network Analyzer,” which is incorporated herein by reference. U.S. Pat. No. 5,642,039 describes components for generating incident test signals and receiving reflected signals that enable the VNA to be light weight and small sized so that it can be handheld. Components for the Site Master™ model S331 are shown in FIG. 1.
The components of FIG. 1 include an RF source 2 and an LO source 4. One embodiment of components making up the RF source 2 and LO source 4 are described in U.S. Pat. No. 5,642,039, where the RF and LO sources 2 and 4 are interconnected and driven by a single oscillator. The RF source 2 is shown in FIG. 1 to have a 25 MHz to 3.3 GHz range to provide a 25 MHz to 3.3 GHz test signal at test port 3. The LO source 4 is shown as a unipolar impulse response source for driving harmonic samplers 20 and 22. An impulse response source is used along with harmonic samplers to provide a high frequency LO down conversion, although if lower frequency devices are desired a simple non-impulse signal source and mixers can be used as described in U.S. Pat. No. 5,642,039. Internal components of the harmonic samplers 20 and 22 can include step recovery diodes (SRDs) similar to those described in U.S. Pat. No. 5,708,377 entitled “Low Power Dual Sampler Utilizing Step Recovery Diodes (SRDs),” also incorporated herein by reference.
A power splitter 6 divides a signal from an RF signal source 2 into two parts to provide the incident and reflected test signals. A first RF signal component provided from a first output of the splitter 6 is provided through a reflection bridge 8 to form the test signal at test port 3 to a device under test (DUT). A reflected RF signal from the DUT is then received through the reflection bridge 8 and directed to harmonic sampler 20. The reflection bridge 8 allows very low frequency reflected test signals to be provided to the harmonic sampler. The reflection bridge coupler 9 can be formed from a coaxial cable line with a connected ferrite piece to couple signals to appropriate resistors 11–13. A second output of the splitter 6 is provided as the incident RF signal through pad 10 to an input of harmonic sampler mixer 22. The attenuation values for pad 10 and resistors 11–13 of the reflection bridge 8 are chosen to equalize the amplitude of the incident and reflected signals.
By mixing the incident and reflected RF signals originating from splitter 6 in harmonic samplers 20 and 22 with a signal from LO signal source 4, the samplers 20 and 22 provide reflected and incident IF test signals at their outputs. The outputs of mixers 20 and 22 are connected to respective bandpass filters 30 and 32 and amplifiers to remove extraneous signals from the incident and reflected IF signals. The outputs of the bandpass filters 30 and 32 are then provided to the inputs of synchronous detectors or a digital signal processor (DSP) for analyzing the downconverted incident and reflected signals.
The Site Master™ model S820 has a higher frequency operation range and includes components that are similar to those disclosed in U.S. Pat. No. 5,977,779 entitled “Handheld Vector Network Analyzer (VNA) Operating At A High Frequency By Mixing LO and RF Signals Having Offset Odd Harmonics,” which is incorporated herein by reference. U.S. Pat. No. 5,977,779 describes components for generating the RF and first and second LO test signals (LO1 and LO2) that enable the VNA to remain lightweight and small sized so that it can be handheld. The components described are illustrated in FIG. 2.
The components of FIG. 2 include an RF source 102 along LO1 and LO2 sources 104 and 105. The RF source 102 provides signals through couplers 109, 110 and 112 to harmonic generators 106 and 108, while the first LO, source 104 provides baseband incident and reflected signals from harmonic generators 106 and 108. Internal components of the harmonic generators can in one embodiment include step recovery diodes (SRDs) as described in U.S. Pat. No. 5, 977,779, as well as shown in U.S. Pat. No. 5,708,377, referenced previously. With SRDs in the harmonic generators 106 and 108 having opposing ends connected to the signal path, the signals having even harmonics will be canceled out, and only the odd harmonic signals will provide an output for the harmonic generators. Selection of the appropriate odd harmonics from harmonic generators 106 and 108 enables down conversion to desired output IF frequencies.
To provide a test signal, the output of bipolar source 102 provides the RF signal to a coupling path of the forward coupler 109. A coupling path of the coupler 109 connects to the bipolar source 102. The through path of coupler 109 then connects the termination load 107 to the through path of couplers 110 and 112 to a test port 103. The coupling path of coupler 110 provides a reflected RF signal to a first input of mixer 106. The coupling path of coupler 112 provides an incident RF signal to a first input of mixer 108.
The coupler 109 functions to provide the signal from the bipolar impulse signal source 109 to the test port 126, rather than using a direct connection to the test port 126, to enable a flat power vs. frequency response. The bipolar signal source is used to generate high frequency range signals, such as from 3.3–20 GHz from the test port 103 shown. With higher harmonics and, thus, higher frequency, the output power of the bipolar impulse signal source 102 decreases exponentially, but the response of the coupler 109 provides increasing power with increasing frequency to flatten the frequency vs. power response.
To assure a substantially equal loss is provided by the VNA to the incident and reflected RF signals so that incident and reflected signals can be later compared relative to one another, attenuation pads 120 and 122 are provided between the couplers 110 and 112 and respective mixers 106 and 108.
With mixer 106 mixing the reflected RF signal with a first LO (or baseband) signal from the first LO signal source 104, shown as a square wave source to drive harmonic mixers, an reflected intermediate frequency (IF) signal is provided from mixer 106 to bandpass filter 130. With mixer 110 mixing the incident RF signal with output from first LO signal source 104, a reflected IF signal is provided from mixer 108 to bandpass filter 132. The pass band of filters 130 and 132 are set so that the IF signal will be passed, while remaining harmonics are filtered out.
The output of filter 130 is provided through an amplifier 134 to a first input of mixer 140, while the output of filter 132 is provided through an amplifier 136 to a first input of mixer 142. Second inputs to mixers 140 and 142 are provided from the second LO signal source 105. The outputs of mixers 140 and 142 are provided to synchronous detectors 150 for signal processing to compare the incident and reflected signals and provide a comparison result to a user interface.
Although the Models S331 and S820 shown in FIGS. 1 and 2 separately provide operation over a frequency range of 25 MHz to 20 GHz, it would be desirable for testing some components to provide operation over the entire 25 MHz to 20 GHz frequency range without requiring the purchase of and operation of two separate test devices.